The present invention relates generally to a rotor for rotary machines, and more particularly to an interior-type permanent magnet rotor and method of making.
Interior-type permanent magnet rotors typically comprise a solid or laminated rotor having permanent magnets disposed in the rotor. In addition, interior-type permanent magnet rotors typically combine synchronous and induction characteristics in their rotor structure and may be used in different environments with alternating current so as to provide a generally constant torque output. In addition, the interior-type permanent magnets focus magnetic flux into an air gap between the rotor and a stator. Furthermore, having the permanent magnets disposed in the rotor typically eliminates the need for rotating electrical connections, saves electrical power otherwise expended in exciting a field winding, lessens the amount of internal heat generation in the field winding and increases power density.
The interior-type permanent magnet rotor comprises a plurality of slots that are typically pre-formed in the interior of the rotor (rotor laminations are stamped out during manufacture) so as to allow the permanent magnets to be disposed therein. While this type of rotor construction has proved to be quite reliable, the pre-formed structure of the rotor, in addition to clearance gaps defined between the permanent magnets and the rotor, typically degrade the amount of magnetic flux focused into the air gap between the rotor and stator. The clearance gap between the magnet and the rotor is typically created to facilitate the disposal of the permanent magnet into the rotor. However, a portion of the magneto-motive-force (MMF) produced by the magnet is typically used to overcome the effect of the clearance gap. In addition, the clearance gap adds to the magnetic reluctance in the motor. In some designs, magnetized permanent magnets are typically inserted into the slots in the rotor and handling of such magnetized permanent magnets is difficult because of the forces of attraction between the magnets and steel structures of the rotor.
Accordingly, there is a need in the art for an interior-type permanent magnet rotor having improved magnet retention.
One embodiment of the present invention comprises a rotor assembly comprising a first core portion, wherein the first core portion has at least one first core protrusion, and a second core portion, wherein the second core portion has at least one second core protrusion. The first core portion and the second core portion are configured to be matingly coupled to each other so as to form an assembled rotor assembly. In addition, the rotor assembly comprises a plurality of magnetizable members wherein respective ones of the plurality of magnetizable members are coupled to each of the first core protrusions and coupled to each of the second core protrusions. The plurality of magnetizable members are adapted to be coupled to a magnetizing fixture prior to mating the first and second core portions so as to magnetize the magnetizable members.